In the fabrication of semiconductor or data storage devices, the attainment of high device densities enables the provision of semiconductor or data storage systems that have enhanced functional capacity. Miniaturization involves the scaling down of device dimensions on semiconductor or data storage wafers so that semiconductor or data storage wafers with high device densities can be attained. Scanning electron microscopes can be employed to measure the dimensions of the miniature structures that lie on a semiconductor or data storage wafer during the fabrication process.
High-resolution photolithographic processes allow high-resolution spacing of structures included on a semiconductor chip or data storage head. Moreover, photolithographic processes allow the transfer of patterns that delineate these structures from a source medium to a silicon wafer. Engineers use photolithography in the manufacture of microelectronic chips and thin film heads for magnetic data recording devices. As a part of the process, a light activated film called a photoresist is applied onto a silicon wafer. A mask representing a type of stencil is placed in the optical path of a lithographic system utilizing ultraviolet light or light with even higher resolution transferring the feature image on the mask to the film. Depending on the photoresist types, either the exposed or the non-disposed portion is dissolved during the development and the feature image is exposed. The wafers go through the following etch process and the pattern of circuit pathways are defined. Electronic board manufacturers also use a similar photolithographic process to print some computer circuit boards.
Conventional techniques for defining wafer structures, such as photolithography and etch, can result in structures that have a re-entrant profile. A feature that has a re-entrant profile can have sidewalls that taper inwardly at the bottom. Some conventional systems employ scanning electron microscopes that attempt to measure dimensions of structures that have such aforementioned re-entrant profiles.
A re-entrant profile can cause process complexities. For example, a phenomenon called shadowing can affect the proper execution of deposition processes. Shadowing prevents material from being properly deposited and can result in the formation of voids at the bottom surface of the structure that has the re-entrant profile.
The formation of voids can have serious consequences both to the fabrication process itself and to the devices that result from it. The process can be impaired as subsequent processing steps that rely on void free surfaces can be deleteriously affected. Moreover, the voids can result in device defects that impair the performance of the devices that result from the process.
FIG. 1 shows a conventional critical dimension-scanning electron microscope (CD-SEM) system 100 that is used to measure and/or image structures that have a re-entrant profile. System 100 includes a chamber 101 that houses a wafer 103. An electron beam 105 that is generated by components of system 100 may be directed from an electromagnetic or electrostatic lens 113 to the wafer 103 at different angles relative to the wafer 103. The electron beam is created from high voltage that is supplied from power supply 111 and is associated with beam generating system 109 that includes emission element 107. Structures 123 and 125 have a re-entrant profile and are scanned with electron beam 105 to obtain data that is used in an attempt to determine a dimension (e.g., height) of structures 123 and 125.
Many of the conventional methodologies that attempt to ascertain the critical dimensions of structures such as structures 123 and 125 that lie on wafers fail to adequately detect and measure the re-entrant profiles of the structures and spaces that lie thereon. One such conventional approach creates or identifies features on the wafer near the structure that is being measured as a means of generating information that is necessary to the dimension measurement process.
Another conventional approach measures the intensity of the light that is reflected from a surface of a structure on the wafer that is being measured as a means of determining the angle of the surface from which it is reflected. These conventional critical dimension measurement methodologies embody inefficient and often inaccurate measurement techniques that can require wasteful process changes and/or steps in order to execute.